PTL 1 discloses, as a lash adjuster configured as mentioned above, a configuration in which a plunger is slidably fitted into a tubular body at an end portion of a rocker arm, a high-pressure chamber that operates the plunger in a projecting direction by oil being supplied to the high-pressure chamber is formed within the body, and a check ball that opens and closes a small hole that is in communication with the high-pressure chamber is provided.
In PTL 1, the plunger is caused to project and abut against the upper end of a valve stem by the oil being supplied to the high-pressure chamber so as to eliminate a gap, and thus generation of a knocking sound is suppressed. When a pressure force from the rocker arm is transmitted to the valve stem, the check ball suppresses an outflow of the oil from the high-pressure chamber, and therefore opening of the valve is realized.